Effective analysis of a microstrip slot coupler

A popular feeding technique for printed antennas is the use of a coupling slot. From a modelling point of view, we can describe the patch as a transmission line resonator and therefore consider this slot as a coupler between two microstrip lines. In this paper we propose a model for such a transverse coupling slot cut in the ground plane between two microstrip lines. Aim of this work is to give an effective and accurate characterization of the electromagnetic coupling due to the slot. The presented approach is based on the equivalence between a microstrip line and a magnetic wall waveguide. The coupling slot effect has been modelled using a full-wave method of moment analysis technique, which takes rigorously into account the effect of the finite thickness of the ground plane. The proposed model has been validated through comparison with both a finite element method and a method of moment-based commercial software. A suitable circuital model has eventually been derived.